quantitative anaylisis

Question 1

how can the concentration of a solution be measured

Answer 1

mols per dm3

Question 2

how do you calculate moles of solute in a given volume of a known concentration

Answer 2

moles = conc x vol

Question 3

when you have a smaller volume or large number of moles of solute what happens to the concentration

Answer 3

a smaller volume or larger number of moles of solute gives a higher concentration

Question 4

when you have a large volume or small number of moles of a solute , what happens to the concentration ?

Answer 4

a larger volume or smaller number of moles of solute gives a lower concentration

Question 5

to get from g/dm3 to mol/dm -3 what will you do

Answer 5

divide by molar mass in grams

Question 6

to et frommol/dm -3 to g/dm3

Answer 6

multiply by molar mass in grams

Question 7

to Carry out an accurate acid-alkali titration, using
burette, pipette and a suitable indicator what is the first step

Answer 7

add acid to the burret using a funnel and make sure to record the volume of the burette to start

Question 8

to Carry out an accurate acid-alkali titration, using
burette, pipette and a suitable indicator what is the second step

Answer 8

add known volume of alkali to a conical flask and add some indicator

Question 9

to Carry out an accurate acid-alkali titration, using
burette, pipette and a suitable indicator what is the third step

Answer 9

place conical flask on white tile (so you can see colour change clearly)

Question 10

why do you place the concial flask on a white tile

Answer 10

so you can see the colour change more clearly

Question 11

to Carry out an accurate acid-alkali titration, using
burette, pipette and a suitable indicator what is the fourth step

Answer 11

add acid to alkali until you reach the end point

Question 12

to Carry out an accurate acid-alkali titration, using
burette, pipette and a suitable indicator, what is the fifth step

Answer 12

calculate how much acid has been added (titre)

Question 13

to Carry out an accurate acid-alkali titration, using
burette, pipette, and a suitable indicator what is the sixth step

Answer 13

repeat until you get concordant results

Question 14

why do we do titrations

Answer 14

to know the exact volume of an acid that reacts with the exact volume of alkali

Question 15

if you only knew the concentration of the acid and wanted to calculate theconcentration of the alkali what would you do ?

Answer 15

• calculate moles of acid using
  moles = concentration x volume
  ○ calculate the mole ratio of acid to alkali using the equation for the reaction
• work out how many moles of alkali you have using the mole ratio and moles of acid
  for example: if you have 5 moles of acid and the ratio of acid to alkali is 1:2, you will have 10 moles of alkali
• calculate the concentration of the alkali using concentration = mol divided by volume
• follow the same method for if you have both concentrations but only one volume

Question 16

what is the equation for percentage yirld

Answer 16

Percentage yield = amount of product produced / maxium amount of product possible x 100

Question 17

how is the amount of product obtaind

Answer 17

Amount of product obtained is known as yield

Question 18

what are causes of actual yield being less than theoretical yield

Answer 18

• incomplete reactions (not all of the reactants have reacted)
  ○- practical losses during the experiment (some product has been left in the weighing boat etc)
  ○ side reactions (some of the products react to form other products than those you wanted

Question 19

what is atom economy

Answer 19

a measure of the amount of starting materials that end up as useful products

Question 20

why is it important for reactions with high atom economy

Answer 20

Important for sustainable development and for economic reasons to use reactions with high atom economy

Question 21

how do you calculate atom economy

Answer 21

atom economy
= (Mr of desired product from reaction/sum of Mr of all reactants) x 100

Question 22

Explain why a particular reaction pathway is chosen to produce a specified product, given appropriate data such as atom economy,yield, rate, equilibrium position and usefulness of by-products